Sigma announced that their way overpriced SD1 DSLR, will soon have an MSRP of $3,300 (down from $7,000).
The SD1 is a unique camera with a unique sensor. It has 15.4 megapixels on an APS-C sized sensor, but the way it records red, green and blue data (in three separate layers) is much different than other sensors, giving it an equivalent of 46 megapixels.
What is interesting is that this price reduction is announced at the same time Nikon announced the 36 megapixel full-frame D800, which will retail for $3,000. The folks at Sigma must believe that these two cameras will be in direct competition with each other. Certainly there will be plenty of comparisons in the coming months.
Because the sensor inside the SD1 is so unique, it's hard to know if the Sigma or Nikon camera produces better images. Somebody (probably lots of somebodies) will do a side-by-side study and determine which one is better. I'm sure both cameras produce great image quality, and the differences are minor. Both cameras produce images with resolution much higher than what most photographers need.
One disadvantage of the SD1 is that, because of how it records data, it takes the camera a long time (up to one minute, but typically less than that) to process and record just one image. The SD1 is not a good choice for wedding, portrait, sports, or wildlife photographers. It is, however, a good choice for landscape and architectural photographers. Basically, you don't want to use this camera in situations where the environment is changing quickly.
Another disadvantage of the SD1 is that it doesn't record video. This may or may not matter to you, but if you want a high-quality video camera, the D800 is the obvious choice.
One advantage of the SD1 (or, really, two advantages) is that the IR filter is also a removable dust protector. With ease, this camera converts to an infrared camera, which is unique in the digital world. If you do or plan to do infrared photography, the SD1 is the best camera on the market for this, hands down. (The second advantage is that dust removal is much, much easier than with other cameras.)
If you are trying to decide between the Sigma SD1 and the Nikon D800, ask yourself if you plan to do infrared photography. If so, the SD1 is your choice. If not, the D800 is probably a little better.
What's truly amazing about this is that we are talking about image quality that just a couple years ago would have cost well over $10,000. Now it can be had for three grand.
Digital photography truly does get both better and cheaper each year.
So no matter if you choose the SD1 or the D800, two or three years from now a camera will come along that is better and will cost less. 10 years from now, no one will be talking about either of these cameras. That's just the way it is with digital photography.